I have presented you a very complete tutorial about widgets a few weeks ago, but here are a few others to help you manage your widgets easily:

• Creating Widgets in WordPress 2.8 with the Widget API | WooCamp
  A tutorial from Woothemes team, to teach you how to create your own WordPress widgets.
• Kaspars Adds Widget Context To Plugin Repository
  Jeff speaks about two WordPress widget plugins, that can help you to specify where and when widgets are displayed within your WordPress theme. If you are looking for such a plugin, go have a look at Widget Logic and Widget context plugin, they cboth can be really useful!

Manage your newsletters

• Plugin: Create Newsletters with Customized Layout | WordPress Blogging | Blog Perfume
  Another simple but yet great newsletter plugin for WordPress.

• Small Potato Out of Hiding: An Interview with Tung Do

Tutorials and resources

• The complete guide to creating widgets in WordPress 2.8
• The 960 Grid System Toolbox & Resources | Webdesigner Depot

Themes

• Theme: Imagination Fully Customizable WP Theme | WordPress Blogging | Blog Perfume
• WP SLIDER WordPress Theme at Bust A Theme

And a bit of fun!

• Take a Break, Laugh and Waste Some Time! – Creattica Daily